Buffer device with a reserve buffer to accommodate a printing substrate web supplied with varying speed in an electrographic print device

ABSTRACT

In an electrographic printing device, a printed printing substrate web is supplied to post-processing machines with irregular speed. In order to achieve that the post-processing machines receive the printing substrate web with a continuous speed, a reserve buffer is introduced in which based on sensor control, a loop of the printing substrate web is formed such that, in each operating mode of the printing device, the loop fluctuates around a desired position, with the result that sufficient printing substrate web is always contained in the reserve buffer.

BACKGROUND

In the transport of a printing substrate web (for example a paper web) from an input station (for example from a reserve stack of the printing substrate web) to a receiving station (for example a spooling or winding) station for the printing substrate web), problems occur when the printing substrate web must be transported on the transport path with different speeds. In order to then prevent a web break or too-large web loops of the printing substrate web, reserve buffers are provided for the printing substrate web.

An example for this problem cam be found in printing devices, for example electrographic printing devices. In such a printing device, an acceptable print image is only given when a printing substrate web (for example a paper web) is supplied in a taut state to the printing group of the printing device. For this, it is known from U.S. Pat. No. 5,685,471 to provide a loop puller device over which the printing substrate web is directed. The loop puller device comprises a loop puller roller, under spring tension and movable in a predetermined region, via which the printing substrate web is stretched, whereby a reserve buffer for the printing substrate web is formed. In normal operation, the deflection of the loop puller roller is sufficient in order to keep the printing substrate web under tension. However, there are situations in which additional measures are necessary in order to leave the printing substrate web in this state. For these cases, the position of the loop puller roller is gauged and, dependent on its position, a control signal is generated with which a braking device is activated that brakes the printing substrate web such that the tension of the printing substrate web is sustained.

Other cases in which it is necessary to provide a reserve buffer occur, for example, between a printing device and a printing substrate web output stacker or between an input stacker for the printing substrate web and the printing device. An example of this results from U.S. Pat. No. 5,685,471. Between the printing device and post-processing machines (output stacker for the printing substrate web), reserve buffers are necessary in order to have sufficient reserve of printing substrate web upon starting and stopping of the print device in order to be able to correspondingly activate or deactivate (in terms of their functionality) the post-processing machines with temporal decoupling. In particular via the withdrawal for the pages of suitable reprinting necessary in the printing device, in particular in color printing, due to the ramping up at start, reserve measure of printing substrate web must be held until the printing speed has been achieved, in order to prevent a tear of the printing substrate web.

It has been proposed to solve this problem with the aid of what is known as a dancing roller, a roller lying on the printing substrate web such that it is freely guided. When, in operation, a slack of the printing substrate web (a sag of the printing substrate web) occurs, this is drawn into the reserve buffer by the weight of the dancing roller and thus a loop is formed. In order to keep the size of the reserve buffer small, it has furthermore been proposed to combine a plurality of dancing rollers into a frame in order to guide the printing substrate web through the reserve buffer in a meandering manner via deflection rollers.

SUMMARY

It is an object to specify a buffer device and a method for generation of a loop of the printing substrate web in a reserve buffer via which it is ensured that a sufficient reserve of printing substrate web is contained in the reserve buffer, and such that in spite of fluctuating feed of the printing substrate web into the reserve buffer, the printing substrate web can be conveyed from the reserve buffer with continuous speed.

In a method and device for controlling a discharge device in a reserve buffer for a printing substrate web in an electrographic printing device, a loop of the printing substrate web formed by an operating device in the reserve buffer is scanned with regard to its position by sensors that emit sensor signals indicating a position of the loop. Dependent on the sensor signals, with a buffer controller the discharge device is regulated such that the loop of the printing substrate web, independent of a speed of supply of the printing substrate web into the reserve buffer in an adjusted state, always fluctuates around a desired position scanned by a sensor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an embodiment of a reserve buffer for the printing substrate web;

FIG. 2 is a principle arrangement of the buffer device made up of the reserve buffer and a buffer controller;

FIG. 3 shows a curve of the movement of the printing substrate web given start-stop operation at the input of the reserve buffer (upper curve) and the curve of the movement of the printing substrate web at the output of the reserve buffer (lower curve);

FIG. 4 is a diagram of the movement of the dancing rollers given a first operating mode of the printing device; and

FIG. 5 shows a diagram of the movement of the dancing rollers given a change of the operating mode of the printing device.

DESCRIPTION OF THE PREFERRED EMBODIMENT

For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the preferred embodiment illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated device, and/or method, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur now or in the future to one skilled in the art to which the invention relates.

Via the sensors, for example light barriers, the discharge device can be controlled such that, in spite of a feed of the printing substrate web with differing speed, for example given start-stop operation of the printing device, the printing substrate web can be transported from the reserve buffer with continuous speed. Post-processing machines can then be used without problems, i.e. they do not have to adapt their operating speed to the speed with which the printing substrate web leaves the printing device.

It is appropriate when three sensors are arranged in the reserve buffer in the loop direction such that the first sensor indicates (first sensor signal) whether the reserve buffer is empty, the second sensor indicates (second sensor signal) whether the loop of the printing substrate web is in the desired position state, and the third sensor indicates (third sensor signal) whether the reserve buffer is full. These sensor signals can be supplied to a buffer controller, for example a microprocessor, that controls the discharge device such that the loop of the printing substrate web fluctuates around the desired position.

The buffer controller can furthermore control the discharge device such that,

-   -   this operates with higher speed when the third sensor indicates         (with the third sensor signal) that the reserve buffer is full,         and maintains this speed until the second sensor indicates that         the loop is in the desired position,     -   this operates with lower speed when the first sensor indicates         (with the first sensor signal) that the reserve buffer is empty,         and maintains this speed until the second sensor indicates that         the loop has reached the desired position,     -   this operates with median speed, dependent on the operating mode         of the printing device, when the second sensor indicates that         the loop is in the desired position.

The median speed essentially depends on the operating mode of the printing device. The speed fluctuations of the printing substrate web occurring in operation can be intercepted by the buffer controller that controls the discharge device such that

-   -   a) this initially operates with median initial speed, dependent         on the operating mode, upon the loop of the printing substrate         web reaching the desired position,     -   b) given an under-run of the desired position by the loop in the         direction towards the third sensor, the speed is increased until         the loop of the printing substrate web crosses the desired         position in the direction towards the first sensor, and then the         speed is lowered again,     -   c) step b) is implemented until the duration in which the loop         is located over the desired position coincides with the duration         in which the loop is located below the desired position, and the         speed then achieved is maintained as an average operating speed.

At the beginning of the printing, the buffer controller controls the discharge device such that, after the start, the discharge device starts after a delay and operates with the speed that corresponds to the average initial speed.

FIG. 1 shows a reserve buffer VP for a printing substrate web 1 as a part of a buffer device PE that is shown in FIG. 2. The reserve buffer VP can be arranged between pre- or post-processing machines MA1, MA2. From a pre-processing machine MA1, for example an electrographic printing device, the printing substrate web 1 is supplied to the reserve buffer VP with varying speed, for example in the start-stop operation. The reserve buffer VP now ensures that the printing substrate web 1 is fed with continuous and optimally equal speed to a post-processing machine MA1, for example a spooling roller. The post-processing machine MA2 can then be operated with constant speed, thus requiring no elaborate controller.

The reserve buffer VP comprises an operating device, for example dancing rollers (in FIG. 1 two dancing rollers 10) that can be rigidly coupled with a frame 11 such that the dancing rollers 10 execute a movement in the same direction. The printing substrate web 1 is supplied to the reserve buffer VP via a movable first deflection roller 12-1 and deflected into the reserve buffer over further fixed deflection rollers 12-2, 12-3, 12-4. Respectively one dancing roller is arranged between the deflection rollers 12-2, 12-3, and 12-4. When printing substrate web 1 is supplied to the reserve buffer VP, via their weight the dancing rollers 10 draw the printing substrate web 1 into the reserve buffer VP and form loops 19. The size of the loops 19 depends on at which speed a discharge device 16 with a motor 17 draws the printing substrate web 1 from the reserve buffer VP. When more printing substrate web 1 is delivered into the reserve buffer VP than is conveyed from the reserve buffer VP by the discharge device 16, the loop 19 wanders into the reserve buffer VP and becomes longer; in the reverse case, the loop 19 is shortened. The movement directions of the dancing rollers 10 is identified with an arrow 18.

It is now a goal of the preferred embodiment to ensure, independent of the rate of the feed of printing substrate web 1 into the reserve buffer VP, that the discharge device 16 always draws the printing substrate web 1 at a nearly constant speed from the reserve buffer VP and supplies it to post-processing machines with optimally constant speed. In order to achieve this goal, sensors (in FIG. 1 the location of the sensors is only indicated), advantageously three sensors, are arranged in the reserve buffer VP. A first sensor 13 is arranged such that it indicates (via its sensor signal LS1) whether the reserve buffer VP is empty, thus the end of the loop 19 does not cover the sensor 13. A second sensor 14 emits a second sensor signal LS2 that indicates whether the end of the loop 19 runs past the sensor 14; the sensor signal LS2 thus indicates whether the loop 19 is in the desired position. Finally, a third sensor 15 emits a sensor signal LS3 that indicates whether the end of the loop 19 covers the sensor 15, thus indicating the reserve buffer VP is full.

With the aid of the sensor signals LS1 through LS3, the discharge device 16 can now be controlled such that the end of the loop 19 fluctuates around the desired position. For example, the sensor signal LS1 indicates that the reserve buffer VP is not empty, and the sensor signal LS3 indicates that the reserve buffer VP is not full. In this state, the end of the loop 19 can fluctuate around the desired position such that the sensor signal LS2 indicates whether the end of the loop 19 crosses or under-runs the sensor 14.

The sensor signals LS1 through LS3 are fed to a buffer controller 20 (FIG. 2) that regulates (dependent on the sensor signals LS1 through LS3) the discharge device 16, and thus its motor 17, such that the end of the loop 19 fluctuates around the desired position. It is then ensured that sufficient reserve of printing substrate web 1 is always contained in the reserve buffer VP, such that printing substrate web can be drawn from the reserve buffer VP with continuous speed without the “empty” state of the reserve buffer VP being able to occur. The buffer controller 20 can be a microprocessor of typical design that is programmed such that it (dependent on the sensor signals LS1 through LS3) emits a control signal RS that is supplied to the motor 17 that transports the printing substrate web 1 from the reserve buffer VP with a speed for which the above-illustrated behavior results.

Curves result from FIG. 3 that show the speed of the printing substrate web 1 plotted over time t at the input of the reserve buffer VP (upper curve) and at the output of the reserve buffer VP (lower curve). From FIG. 3 it is visible that the printing substrate web 1 is fed to the reserve buffer VP at significantly varying speed; for example, there are standstill times ts and times tn in which the speed rises or falls according to a ramp and times tk in which the speed is constant and times ta in which the speed is negative, thus printing substrate web 1 is pulled back from the reserve buffer VP. This very different behavior in the movement of the printing substrate web 1 at the input of the reserve buffer VP must now be compensated by a regulated operation of the discharge device 16 and be converted into a movement of the printing substrate web 1 corresponding to the lower curve. The discharge device 16 is regulated such that at the beginning of the operation the speed of the discharge device 16 increases (ramp tr) and then remains approximately constant (curve td).

The behavior of the dancing rollers 10 in the reserve buffer VP results from FIG. 4, when the printing device operates in a first operating mode (mode 1) and printing substrate web 1 is fed to the reserve buffer VP corresponding to FIG. 3, upper curve. If the reserve buffer VP is initially empty, the dancing rollers 10 are located in the “empty” position (indicated by the sensor signal LS1) in the buffer. The discharge device 17 initially operates with a delay with an average start speed dependent on the operating mode. The result is that the dancing rollers 10 migrate into the reserve buffer VP as long as they (and with them the end of the loop 19) pass by the sensor 14 and cover this (indicated by the sensor signal LS2). If the dancing rollers 10 run downwards past the sensor 14 and under-run the desired position, dependent on the sensor signal LS2 the speed of the discharge device 16 is increased until the dancing rollers 10 again cross the sensor 14 and the sensor signal LS2 therewith correspondingly changes. The dancing rollers 10 are then again located above the desired position. Now the speed is lowered. The result of this regulation of the discharge device 16 is that the dancing rollers 10 pivot around the desired position. The speed of the discharge device 16 is only no longer changed when the duration in which the dancing rollers 10 are located above the desired position coincides with the duration in which the dancing rollers 10 are located below the desired position. The speed of the discharge device 16 then achieved establishes the average operating speed of the discharge device 16.

When, in the same operating mode printing substrate web 1 of a different format is printed, the relationships in the feed of printing substrate web 1 to the reserve buffer VP changes. FIG. 4 (point in time t0) likewise shows this. The result of this change is that the dancing rollers 10 wander over or under the desired position, and the average operating speed must be changed. The procedure corresponds to the operating method specified above, i.e. the speed of the discharge device 16 is increased or decreased until the duration of the dancing rollers 10 above the desired position and below the desired position is the same again. The speed that has then been set is further used as an operating speed.

From FIG. 5, the case results that in the print operation the operating mode is changed with the result that the supply of printing substrate web 1 in the reserve buffer VP significantly changes. Initially, the first operating mode (mode 1) operated as shown in FIG. 4. The adapting behavior of the discharge device. 16 corresponds to that in FIG. 4. At the point in time t1, the operating mode of the printing device is changed (from mode 1 to mode 2). In the example, more printing substrate web is transported into the reserve buffer VP. Since the operating speed initially remains the same, the dancing rollers 10 (and therewith the loop 19) wander downwards in the reserve buffer VP until the dancing roller 10 cover the sensor 15, such that the sensor changes the sensor signal LS3. Due to this, the buffer controller 20 significantly increases the speed of the discharge device 16 until the dancing rollers 10 again cross over the sensor 14 and this changes the sensor signal LS2. The discharge device 16 subsequently operates further with an average operating speed, adapted to the new operating mode, that is corrected in the further course as this has been shown in FIG. 4. The behavior of the buffer device PE is corresponding when the change of the operating mode leads to less printing substrate web 1 being fed into the reserve buffer VP. The dancing rollers 10 then cross the sensor 13, which changes the sensor signal LS1 with the result that the buffer controller 20 lowers the speed of the discharge device 16 until the dancing rollers 10 under-run the desired position. The adjustment of the average operating speed in the discharge device 16 then occurs again.

With this regulation of the discharge device 16, it is thus achieved that a reserve of printing substrate web 1 is always present in the reserve buffer VP that is sufficient in order to ensure a continuous delivery of printing substrate web 1 to a subsequent device MA2. These devices can operate without being deactivated and are thus decoupled from operation of the printing device and require no elaborate control.

While a preferred embodiment has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiment has been shown and described and that all changes and modifications that come within the spirit of the invention both now or in the future are desired to be protected. 

1. A buffer device with a reserve buffer for accommodation of a printing substrate web supplied with varying speed in an electrographic print device, comprising: at least one operating device arranged in the reserve buffer, an operating force of the operating device acting on the printing substrate web in order to form a loop of the printing substrate web; sensors scanning the loop arranged in the reserve buffer that emit sensor signals indicating a length of the loop; and a discharge device controlled by the sensor signals which conveys the printing substrate web with continuous speed from the reserve buffer.
 2. A buffer device according to claim 1 in which the operating device comprises at least one movable dancing roller.
 3. A buffer device according to claim 2 in which two of said dancing rollers are provided that are rigidly coupled with one another via a connection web.
 4. A buffer device according to claim 1 in which three sensors are arranged in a loop direction in the reserve buffer such that the first sensor displays whether the reserve buffer is empty; the second sensor indicates whether the loop of the printing substrate is in a desired position; and the third sensor indicates whether the reserve buffer is full.
 5. A buffer device according to claim 1 in which the sensors comprise light barriers.
 6. A buffer device according to claim 4 in which a buffer controller, is provided to which the sensor signals are supplied and which controls the discharge device such that the loop fluctuates around the desired position.
 7. A buffer device according to claim 6 in which the buffer controller controls the discharge device such that it operates with a higher continuous speed when the third sensor indicates with a third sensor signal that the reserve buffer is full, and maintains this continuous speed until the second sensor indicates that the loop is in the desired position; operates with a lower continuous speed when the first sensor indicates with a first sensor signal that the reserve buffer is empty, and maintains this continuous speed until the second sensor indicates that the loop has reached the desired position; and operates with an average continuous speed, dependent on an operating mode of the printing device, when the second sensor indicates that the loop is in the desired position.
 8. A buffer device according to claim 7 in which the buffer controller controls the discharge device such that it operates with an average starting speed, dependent on the operating mode, upon the loop reaching the desired position; given an under-run of the desired position by the loop in a direction towards the third sensor, the speed is increased until the loop crosses the desired position in a direction towards the first sensor, and then the speed is lowered again; and a speed at which a duration in which the loop is located over the desired position coincides with a duration in which the loop is located below the desired position is maintained as an average operating speed.
 9. A buffer device according to claim 8 in which the buffer controller controls the discharge device such that, after a start of the printing device, the discharge device operates after a delay with a speed that corresponds to the average starting speed.
 10. An electrographic printing device, comprising: a printing device supplying a printed substrate supplied with varying speed from the printing device; a buffer device following the printing device; and said buffer device comprising at least one operating device, an operating force of the operating device acting on the printing substrate web in order to form a loop of the printing substrate web, sensors scanning the loop arranged in the buffer that emits sensor signals indicating a length of the loop, and a discharge device controlled by the sensor signals which conveys the printing substrate web with continuous speed from the buffer device.
 11. An electrographic printing device according to claim 10 in which the buffer device is arranged within the printing device.
 12. A method for controlling a discharge device in a reserve buffer for a printing substrate web in an electrographic printing device, comprising the steps of: scanning a loop of the printing substrate web formed by an operating device in the reserve buffer with regard to its position by sensors that emit sensor signals indicating a position of the loop; and dependent on the sensor signals, with a buffer controller regulating the discharge device such that the loop of the printing substrate web, independent of a speed of supply of the printing substrate web into the reserve buffer in an adjusted state, always fluctuates around a desired position scanned by a sensor.
 13. A method according to claim 12 in which the buffer controller regulates the discharge device dependent on the sensor signals emitted by first, second, and third sensors arranged in a loop direction in the reserve buffer such that the discharge device operates with higher speed when the third sensor indicates with a respective sensor signal that the reserve buffer is full, and maintains this speed until the second sensor indicates with a respective sensor signal that the loop has achieved the desired position; operates with lower speed when the first sensor indicates with a respective sensor signal that the reserve buffer is empty, and maintains this speed until the second sensor indicates with its sensor signal that the loop has reached the desired position; and operates with average speed, dependent on an operating mode of the printing device, when the second sensor indicates that the loop is in the desired position.
 14. A method according to claim 13 in which the buffer controller regulates the discharge device such that it operates with average initial speed, dependent on the operating mode, upon the loop reaching the desired position; given an under-run of the desired position by the loop in a direction towards the third sensor, the discharge device increases the speed until the loop crosses the desired position in a direction towards the first sensor, and then the speed is lowered again; and the discharge device maintains as an average operating speed a speed at which a duration in which the loop is located over the desired position coincides with a duration in which the loop is located below the desired position.
 15. A method according to claim 14 in which the buffer controller regulates the discharge device such that, after a start of the printing device, the discharge device operates after a delay with a speed that corresponds to the average starting speed.
 16. A method according to claim 12 wherein a buffer device is provided with said reserve buffer.
 17. A buffer device for accommodation of a printing substrate web supplied with varying speed in an electrographic print device, comprising: at least one operating device, an operating force of the operating device acting on the printing substrate web in order to form a loop of the printing substrate web; at least one sensor scanning the loop arranged in the reserve buffer that emits sensor signal indicating a position of the loop; and a discharge device controlled by the sensor signal which conveys the printing substrate web with adjustable continuous speeds from the buffer.
 18. A method for controlling a printing substrate web output from a printing system of an electrographic printing device, comprising the steps of: forming a loop of the printing substrate web with an operating device in contact with the loop and determining a position by at least one sensor that emits a sensor signal indicating a position of the loop; and dependent on the sensor signal, regulating a discharge device to convey the printing substrate web with adjustable continuous speeds from the buffer. 